Sudden cardiac death represents a common cause of death. Numerous studies have shown that, in the vast majority of cases, sudden cardiac death is caused by rapid abnormalities in the cardiac rhythm.
In the German Zeitschrift fur Kardiologie [Journal of Cardiology], 78:5, (1989), pages 55 through 62, there are references from which it can be concluded that in approximately one-half to one-third of the cases, a life-threatening abnormality in the cardiac rhythm is triggered by a transitory deficiency in the heart's blood supply--the so-called myocardial ischemia. As a rule, when this occurs the deficiency in the blood supply precedes the abnormality in the cardiac rhythm by several minutes and leads to an instability of the electrical propagation of the excitation of the heart muscle, with the danger that the life-threatening abnormality in the cardiac rhythm will be triggered. When this occurs, it is only in a relatively few cases that the victim himself perceives this as pain symptoms which could serve as a possible motivation to countermeasures such as interruption of physical activity, taking medication, or seeing a doctor.
It is known from DE-38 18 136 A1 that implantable defibrillation systems can be provided to combat abnormalities in the cardiac rhythm. In such cases, a defibrillator is usually implanted in the abdomen and defibrillator electrodes are run from it to the heart. These are placed, respectively, in the area of the right ventricle and the right auricle or the transition to the superior vena cava. If necessary, surface electrodes can also be placed against the outside of the heart in order to be able to transmit the high energy needed for the defibrillation. When this is done, the detection of an abnormality in the cardiac rhythm is carried out by means of the electrode in the right ventricle, whereby a difference in the electrical potential between two points in the apex of the heart, which are separated from each other by about one-half centimeter to one centimeter, is derived or measured.
This type of a difference in potential arises with each heartbeat because of the electrical propagation of the excitation of the heart which precedes it. When specific intervention criteria have been reached, the control unit of the defibrillator releases the appropriate treatment program and eliminates the disturbance in the cardiac rhythm by means of the purposeful delivery of precise pulses. In the majority of cases when this is done, the delivery of an electrical shock of from two to forty joules is necessary. This leads, in known manner, to an electrical rectification of all heart muscle cells and thus to the restoration of the normal heartbeat.
Since implanted systems of this type have only a limited energy capacity in the built-in battery, only a limited number of such defibrillation shocks can be delivered, after which an operative exchange is necessary. Thus, the less often there are abnormalities in the cardiac rhythm, the longer the device in question can remain inside the patient and the less danger there is for the patient himself that when a life-threatening abnormality in the cardiac rhythm occurs, it will no longer be possible to remedy it.